Distribution of Bioavailable Nitrogen and Phosphorus Forms and Their Relationship in the Sediments of Dianchi Lake

The distribution of bioavailable nitrogen and phosphorus forms in eight sampling sites from surface sediments of Dianchi Lake was analyzed by chemical sequential extraction methods,and their relationships were also discussed. The results showed that the distribution of w(TP) and w(TN) varied significantly by spatial location. Due to mining of phosphorite and external pollution inputs, the contents of TP and TN were high in the northern and southern parts of Dianchi Lake. In the middle part,the contents of TP and TN were relatively low because of the influence of hydrodynamic force. The bioavailable nitrogen and phosphorus in the sediments consisted of four forms: ion exchangeable nitrogen and phosphorus (IEF-N,IEF-P),weak acid extractable nitrogen and phosphorus (WAEF-N, WAEF-P),strong alkali extractable nitrogen and phosphorus ( SAEF-N,SAEF-P),and strong oxidant extractable nitrogen and phosphorus (SOEF-N,SOEF-P). The relative contents of different bioavailable nitrogen and phosphorus forms ranked according to the following sequence: w ( SOEF-N ) ( 68. 1%-78. 8% ) w ( IEF-N ) ( 10. 1%-14. 9% ) w ( WAEF-N ) ( 5. 8%-8. 9% ) ≈ w(SAEF-N) (5. 3%-8. 7% ),and w( SAEF-P) (68. 6%-75. 2% ) w( SOEF-P) (23. 4%-30. 0% ) w( WAEF-P) (0. 6%-1. 8% ) w ( IEF-P ) (0-0. 1% ). There was a positive correlation between bioavailable nitrogen and phosphorus forms, indicating the same trend of transfer and transformation. The ratio of bioavailable nitrogen to phosphorus in the same extractant was also analyzed; the results suggested that the different bioavailable nitrogen and phosphorus forms influenced the mineralization and release rate of nitrogen and phosphorus in the sediments.